Patch "scsi: don't BUG_ON() empty DMA transfers" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

scsi: don't BUG_ON() empty DMA transfers

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
scsi-don-t-bug_on-empty-dma-transfers.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Johannes Thumshirn <[email protected]>
Date: Tue, 31 Jan 2017 10:16:00 +0100
Subject: scsi: don't BUG_ON() empty DMA transfers

From: Johannes Thumshirn <[email protected]>

commit fd3fc0b4d7305fa7246622dcc0dec69c42443f45 upstream.

Don't crash the machine just because of an empty transfer. Use WARN_ON() combined with returning an error.

Found by Dmitry Vyukov and syzkaller.

[ Changed to "WARN_ON_ONCE()". Al has a patch that should fix the root
cause, but a BUG_ON() is not acceptable in any case, and a WARN_ON() might still be a cause of excessive log spamming.

NOTE! If this warning ever triggers, we may end up leaking resources, since this doesn't bother to try to clean the command up. So this WARN_ON_ONCE() triggering does imply real problems. But BUG_ON() is much worse.

People really need to stop using BUG_ON() for "this shouldn't ever
happen". It makes pretty much any bug worse. - Linus ]

---
 drivers/scsi/scsi_lib.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -1031,7 +1031,8 @@ int scsi_init_io(struct scsi_cmnd *cmd)
 	bool is_mq = (rq->mq_ctx != NULL);
 	int error;
 
-	BUG_ON(!rq->nr_phys_segments);
+	if (WARN_ON_ONCE(!rq->nr_phys_segments))
+		return -EINVAL;
 
 	error = scsi_init_sgtable(rq, &cmd->sdb);
 	if (error)

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/scsi-don-t-bug_on-empty-dma-transfers.patch